My 2001 grand jeep cherokee code sysyem is erased

hey year and 4.0L stated. wow
so next look it, (posted 100s of times)
WJ jeep, 2001
see emission chapter, see diagnostics, see 1291?

says intake air temp sensor reads wrong, its easy to test
first makesure its plugged in and wires not damaged>

http://www.jeep4x4center.com/knowledge-base/index.htm?utm_source=cj#service

According with your other quesions, the DTC P1491 code is actually radiator fan control relay circuit.
Soft reset if the battery disconnect would have erased the code; the first thing I would replace for that code (fan relay).
Additionally, its possible thta your THEFT system is activated, check owners manual to disarm. Check details here:
- Grand Cherokee fuses

- Diagnostic Trouble Codes

Hope this helps.

IT CAN BE THAT THE FLUID NEEDS TO BE REPLACED. IT GETS OLD AND DO NOT OPERATE CORECTLY .

TRD Communication error:

http://www.readmanual.com/profile/v.cgi?2632.cars/jeep/cherokee/2002
http://www.readmanual.com/profile/v.cgi?2633.cars/jeep/cherokee/2002

Your PCM (engine computer) senses a fault code with an engine management component. You will need a codes reader to retrieve the code. If you you do not have a code reader, go to a well supplied auto supply store like autozone, and they will read the codes and let you know what they are. This would be the first step any Tech would do before diagnostic testing begins.

you need to get the codes read to know why the light is on,

If you do not know what the codes are, it is O2 sensor. This means the computer is not reading the right information from the faulty sensor. (there is a set range the sensor is meant to show, if one goes over or under the computer shows check engine). The diagnostic is not too bad, give the car a tune up, plugs, wires etc. and replace the O2 sensor. This normally clears up any problems. Let me know if you need further clarification or help.

a bad cam sensor will cause vehicle to shut off while driving, and cause a hard time starting. but this usually sets a trouble code p0340. scan vehicle to see if any codes come up. after it is fixed, erase codes with a obd2 scanner. if you do not have one, you can go to any auto parts store and they will erase codes for free.

You can do one of three things.1. buy a scan tool 2. go to a dealer and pay to have the codes read and diagnosed 3. go to your local parts chain to have it read for free. (call first to verify). The code will tell you what system is malfunctioning and what the malfunction is. The parts store option is my choice, because you can also get the part to fix it if needed and you are not out the $ for diagnostics, nor did you need an appt to get it in.